A+ A− B

Side Angle Side Postulate

Proving Congruent Triangles with SAS

The Side Angle Side postulate (often abbreviated as SAS) states that if two sides and the included angle of one triangle are congruent to two sides and the included angle of another triangle, then these two triangles are congruent.
Example 1  
    $$ \triangle ABC \cong \triangle XYZ $$
  • Two sides and the included angle are congruent
    • AC = ZX  (side)
    • $$ \angle $$ACB = $$ \angle $$XZY  (angle)
    • CB = ZY   (side)
  • Therefore, by the Side Angle Side postulate, the triangles are congruent.
  • Side Angle Side Postulate

Included Angle

The included angle means the angle between two sides. In other words it is the angle 'included between' two sides.
Identify Side Angle Side Relationships
In which pair of triangles pictured below could you use the Side Angle Side postulate (SAS) to prove the triangles are congruent?

Identify SAS Postulate and theorem
Side Angle Side example
SAS postulate

 Side Angle Side Practice Proofs  

Given: 1) point C is the midpoint of BF 2) AC= CE

Prove that $$ \triangle ABC \cong \triangle $$EFC

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Side Angle Side Example Proof

Prove $$ \triangle BCD \cong \triangle BAD $$

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Given: HJ is a perpendicular bisector of KI

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Side Angle Side Activity

Below is the proof that two triangles are congruent by Side Angle Side.

Can you imagine or draw on a piece of paper, two triangles, $$ \triangle BCA \cong \triangle XCY $$ , whose diagram would be consistent with the Side Angle Side proof shown below?
Show Two Triangles